Free radical emulsion polymerizations are used to form most synthetic latexes. While ethylene can be polymerized by free-radical mechanisms, ethylene-propylene copolymers cannot be commercially prepared by free radical polymerization. Instead ethylene-propylene (EPM) copolymers and ethylene-propylene-diene copolymers are made by a coordination polymerization solution method rather than free radical emulsion processes. Examples of coordination polymerization methods are Ziegler-Natta polymerization and metallocene polymerization.
Emulsions or dispersions of preformed polymers have been made by dissolving the bulk polymer in a solvent to reduce its viscosity and emulsifying it in water, often with the aid of a dispersant such as a surfactant. Thereafter, the solvent is removed. Such processes are described in Preparation of Artificial Latexes by G. W. Burton and C. P. O'Farrell in J. of Elastomers and Plastics, vol. 9, January 1977, pp 94-101. While such processes to dissolve a bulk polymer and emulsify it to form an artificial latex sound like a simple procedure, there are many impediments to forming artificial latexes with useful properties, including high processing costs.
Bulk EPDM polymer has been functionalized with a variety of monomers (such as maleic anhydride) and used in preparing various polymer blends. Bulk EPDM refers to EPDM polymer without solvents or water.